How to safely erase hdd and reinstall?

BLBL

macrumors 6502a
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Apr 11, 2018
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Mac OS newbie here, so bear with me. :)
Seems to be more life in this side of the forum, so I'll ask here if anyone knows better.
I have MBA 2018 I'd like to format internal hdd and reinstall OS so that it will be exactly like when it was new.

What would be easiest way to do it and is there any way to do it so that factory display calibration does not get lost (should I backup it before formatting and where it can be found)?

There was no restore media with the machine, but is there a hidden restore partition in HDD (and does it contain correct/calibrated display profile)?
 

chrfr

macrumors G3
Jul 11, 2009
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Mac OS newbie here, so bear with me. :)
Seems to be more life in this side of the forum, so I'll ask here if anyone knows better.
I have MBA 2018 I'd like to format internal hdd and reinstall OS so that it will be exactly like when it was new.

What would be easiest way to do it and is there any way to do it so that factory display calibration does not get lost (should I backup it before formatting and where it can be found)?

There was no restore media with the machine, but is there a hidden restore partition in HDD (and does it contain correct/calibrated display profile)?
The "Factory calibration" does not involve a profile stored on the disk. Reinstalling the OS will not affect color.
 

BLBL

macrumors 6502a
Original poster
Apr 11, 2018
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Thanks for your replies!

The "Factory calibration" does not involve a profile stored on the disk. Reinstalling the OS will not affect color.
OK, so factory calibration is hardware based or is there some way to accidently mess or lose that?
Are ICC-profiles in display/color menu the same in every Mac not matter what model or what panel comes with the machines?

That one of the documents I've been reading before but that does not say where to get installation media once internal hdd is wiped clean by formatting it. Is there hidden partition you cannot delete so that reinstallation is possible or how to make sure I don't end up with empty non bootable machine. And is there some alternative method to download installation packages?
 

Weaselboy

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OK, so factory calibration is hardware based or is there some way to accidently mess or lose that? Are ICC-profiles in display/color menu the same in every Mac not matter what model or what panel comes with the machines?
The profiles are included with the default OS install.

That one of the documents I've been reading before but that does not say where to get installation media once internal hdd is wiped clean by formatting it. Is there hidden partition you cannot delete so that reinstallation is possible or how to make sure I don't end up with empty non bootable machine. And is there some alternative method to download installation packages?
The OS is downloaded over the Internet on newer Macs like yours, so you don't need an install media. Just hold command-option-r at boot then pick your wifi when prompted. You will see a spinning grey globe while the recovery utility is downloaded. Then you will see the recovery screen. From there follow the directions at the link @chabig gave you to erase the entire disk and install the OS.
 

BLBL

macrumors 6502a
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The profiles are included with the default OS install.
OK, so they no not hardware specific in any way. That's good to know and I guess I don't bother even trying to back them up, since everything else I have installed it what I want to get rid off and start from the fresh as it was when I first unboxed it.

The OS is downloaded over the Internet on newer Macs like yours, so you don't need an install media. Just hold command-option-r at boot then pick your wifi when prompted. You will see a spinning grey globe while the recovery utility is downloaded. Then you will see the recovery screen. From there follow the directions at the link @chabig gave you to erase the entire disk and install the OS.
This is good to know and sound like a clever idea not reserving space from the internal HDD for recovery partition as it is often in Windows machines.

Do you or anyone else have any idea should I reset something else like nvram or smc also before doing that to make sure everything gets reset (and those will not affect display factory calibration if I try them also)?

I'm having some color banding isssue with mine and I'm not quite sure if it was like that when I first got it or is it from something I have done. It tried changing gamma in display calibration utility but I made sure to save it under different name and later on even deleted that I created and have been using the original Color LCD profile but no avail.
I'm seeing problem described here: https://en.wikipedia.org/wiki/Colour_banding
Mine shows that in some photos and it is something like what is in those 8bit gradient photos.

I see that happening for example when view the first two photos of Macbooks in this link https://www.apple.com/macbook-pro/
There is this gradient effect surrounding machines in the photos and it is not very smooth when I view that in my Air display. My cheap Zenbook (Windows) and also my desktop with Dell monitor (also Windows), iPad 2018 and iPhone X shows that much smoother.
 

Weaselboy

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Do you or anyone else have any idea should I reset something else like nvram or smc also before doing that to make sure everything gets reset (and those will not affect display factory calibration if I try them also)?
It won't hurt to do that, but it is not really necessary.
 

BLBL

macrumors 6502a
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Yeah, it is vague at the best but luckily looks like everything worked. I emptied whole hdd as instructed and then proceed with MacOs reinstall. It took maybe about 50 minutes and was again up and running. It seems to be missing those Pages, Numbers etc. office apps now but I got them from App Store again so I guess nothing was lost. Also it seemed to created identically named Color LCD icc-profile and it looks pretty much the same as before reinstallation but I took backup of old icc-profiles just in case I could compare files later on to make sure and the files are not completely identical but just few bit different in the beginning of the file.

Also complete reinstallation did not make any difference in gradient banding issue. I'm not completely sure if it was like that when I first got it, or did it change after it did OS update to latest Mojave version than brought extra bump in panel brightness from 300 to 400 nits. Also I'm not sure if colour bit setting in Air 2018 is really supposed to be only 24bit (ARGB8888)?

Full reinstallation seemed to free some HDD space also, because now it is pretty even 100GB free even after installing those office apps. Originally there was just barely over 90GB after initial out of the box setup and Mojave update. Not sure if something is still missing or was that nearly 10GB just garbage.
 
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Weaselboy

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Not sure if something is still missing or was that nearly 10GB just garbage.
This is pretty common. An erase and reinstall like you did wipes any swap and cache files so it is expected there will be less space used. Over time those swap and cache files will rebuild and take back some of that space.
 

BLBL

macrumors 6502a
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This is pretty common. An erase and reinstall like you did wipes any swap and cache files so it is expected there will be less space used. Over time those swap and cache files will rebuild and take back some of that space.
I think you are right. Even mine was brand new but it came with older os version that it automatically updated to latest version the same day I got it, so probably update only will cause some left over data hogging hdd space.

I think startup time has reduced a tiny bit too, but it is still much longer what I expected for a Macbook. I think it is around 20-30 seconds to desktop from powered off state. That's more than in midrange Windows laptops.
 

ApfelKuchen

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This is good to know and sound like a clever idea not reserving space from the internal HDD for recovery partition as it is often in Windows machines.
The on-disk Recovery partition exists, too, for routine system recovery/maintenance purposes - running disk repair, reinstalling the OS, etc. Press and hold Command + R at startup. It's not very clever to depend on an Internet connection for everything.

Internet Recovery is generally considered a backup to the on-disk Recovery partition. If you try to boot to Recovery and the system can't find the onboard Recovery partition, it will automatically try to boot from Internet Recovery.

Outside of failure-to-find-hard-drive, Internet Recovery is most commonly used when you plan to erase the entire HDD (rather than just the Mac boot partition/volume) or are replacing a HDD.

Apple's been using this dual Recovery/Internet Recovery system since OS X 10.7.x, released in 2011.
 

BLBL

macrumors 6502a
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I did it by press and hold Command + R but I first Wiped whole HDD and then went back to restore OS when it started to reinstallation. I did not actually say where it was coming from but I assume it must have been internet based since it took good 30 minutes loading until actual installation started and it seemed to download something when I checked my router statistics for Macbook during that.
Now that what you said makes sense why I have quite a bit more free HDD space than before wiping it, if there was some hidden partition.

Do you or anyone else know how factory display calibration is stored in Macbook's? I mean is there some way to accidently delete it, for example by doing factory reset by wiping HDD? Mine looks pretty much equal as it did before wiping HDD but just like to make sure I did not mess anything or lost something that I haven't noticed yet.

I have Time Machine backup made before I wiped hdd, just in case. This is what my another question is related.
I'd like to retain that backup for future just in case but how to move it to another folder in USB hdd that is used for TM?
I haven't configured TM for use in new installation but when I plug in this USB HDD and try to move old TM backup under new folder it does not allow. I thought I could just keep it under the same HDD but in my own folders to avoid confusion but obviously it is prevented. Please help. :)
 

ApfelKuchen

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Whether you use Internet Recovery or the internal Recovery partition, reinstalling the OS requires a download from the Internet. Internet Recovery needs to download and mount the Recovery disk image before you can start downloading the full OS.

As Weaselboy already said, the difference in the installation size most likely has to do with the absence of cache files, which will get larger over time.

If you erased the entire HDD (including the hidden Recovery partition), the Recovery partition will always be recreated when you reinstall the OS.

Restoring from the Time Machine backup doesn't work the way you think. It is not an all-in-one disk image, it's a set of incremental backups that must be reconstructed by the Time Machine software in the OS. It can be used in three basic ways:

From Recovery/Internet Recovery > Restore from a Time Machine backup. This restores the entire system including OS from the restore point of your choosing.

From Setup Assistant (which loads the first time you boot a new Mac or after an erase/reinstall of the OS like you did), or Migration Assistant (a utility that is run from the regular Mac desktop). Setup Assistant and Migration Assistant do not restore the OS, they restore user configuration, data, and apps from the most recent backup.

From Enter Time Machine - this last mode is used when you're booted into the desktop, and allows you to selectively restore data files from the restore point of your choice (accidental deletions, older versions, etc.)

As to the "factory display calibration" - that's been answered several times. Asking again does not change the answers you've been given.
 
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CoastalOR

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I have Time Machine backup made before I wiped hdd, just in case. This is what my another question is related.
I'd like to retain that backup for future just in case but how to move it to another folder in USB hdd that is used for TM?
I haven't configured TM for use in new installation but when I plug in this USB HDD and try to move old TM backup under new folder it does not allow. I thought I could just keep it under the same HDD but in my own folders to avoid confusion but obviously it is prevented. Please help. :)
Follow the Apple instructions on how to move a previous TM backup to a new drive:
https://support.apple.com/en-us/HT202380
 

BLBL

macrumors 6502a
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As Weaselboy already said, the difference in the installation size most likely has to do with the absence of cache files, which will get larger over time.
I understand your point and that is common reason in Windows too but I don't think in this particular case that was the reason as mine was like that from the start. Not sure what caused that but from what I can tell, I think I got installed everything back as what was there originally when I did wipe the disk and reinstalled os. I had to download "office" apps separately from App Store.

Restoring from the Time Machine backup doesn't work the way you think. It is not an all-in-one disk image, it's a set of incremental backups that must be reconstructed by the Time Machine software in the OS. It can be used in three basic ways:

From Recovery/Internet Recovery > Restore from a Time Machine backup. This restores the entire system including OS from the restore point of your choosing.

From Setup Assistant (which loads the first time you boot a new Mac or after an erase/reinstall of the OS like you did), or Migration Assistant (a utility that is run from the regular Mac desktop). Setup Assistant and Migration Assistant do not restore the OS, they restore user configuration, data, and apps from the most recent backup.

From Enter Time Machine - this last mode is used when you're booted into the desktop, and allows you to selectively restore data files from the restore point of your choice (accidental deletions, older versions, etc.)
So Time Machine backup is mostly just configuration settings and user data/apps, and not compete 1:1 image of whole OS including everything? Does that mean if I wipe disk by booting Command + R and then select restore from Time Machine backup it will basically do Internet installation of OS installation and then just add user data etc. on top of it to make it look identical but something in the OS level/drivers can be different?

If I got that right, then basically my old backup is worthless in terms of possibility to go back to 1:1 in OS level? I had nothing personal data I want to retain included then, so my only purpose for TM backup was to get OS fully backed up and ability to go back 100% same as it was before Wipe HDD / Restore OS. So if that is not possible with it, I can then just as well just format that USB HDD.

As to the "factory display calibration" - that's been answered several times. Asking again does not change the answers you've been given.
Sorry for confusion but I meant I'm interested to know where actual factory display calibration is stored in MacBooks. I don't think I've seen any explanation of that yet, if anyone actually has that information. Obviously it is not any OS level driver or ICC-profile, but where / how it is stored? Is there any individual calibration done for each machine at the factory? or are they simply using certain specs panels that do not need individual calibration? I doubt that latter option is not viable as there tend to be all kind of variation usually from panel to panel due to many factors, difference in backlight led is common.
 
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BLBL

macrumors 6502a
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By they way, it there any good reason not to make external USB hdd used for Time Machine backups not encrypted (and would it be better to format USB HDD as encrypted before adding it to TM, or just make unencrypted drive and just set Time Machine to encrypt backups)? Because I will use that drive also to save other files to it in Mac, I guess it would be better to leave drive itself non encrypted, just in case.

Also does it matter if my MacBook's system drive is not encrypted by Filevault (or what is was called in Mac OS) when using Time Machine in either mode (or do they must match in both)? And same question about system drive, any reason not to turn it on afterwards (I did not make it during initial setup). I guess in possible T2 chip problems that can cause big troubles and maybe some performance issues?
 

Weaselboy

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So Time Machine backup is mostly just configuration settings and user data/apps, and not compete 1:1 image of whole OS including everything?
TM does backup the entire drive so is in effect a clone of the internal drive and it can be used to do a full restore, including the OS, apps, and all data and settings.

If you want your TM backup encrypted, it is much faster to format the external drive to encrypted before using it with TM.

Whether the TM drive or the internal drive are encrypted or not does not matter either way. When you are using the drives they are unlocked, so TM is still just copying data.

On the system drive, you do not want to format to encrypted. Just do a regular format the turn on FileVault afterwards.
 

jdiamond

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I get the feeling all this was a side point: The main point is you did all this because you're having an issue with your GPU and you were hoping a clean install would fix it, but it didn't. I'd consider making a genius bar appointment. I'm quick to point out Apple's faults, but the quality of their screens has always been top notch. If you see a noticeable visual issue, it's worth checking for a GPU problem.
 

ApfelKuchen

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Sorry for confusion but I meant I'm interested to know where actual factory display calibration is stored in MacBooks. I don't think I've seen any explanation of that yet, if anyone actually has that information. Obviously it is not any OS level driver or ICC-profile, but where / how it is stored? Is there any individual calibration done for each machine at the factory? or are they simply using certain specs panels that do not need individual calibration? I doubt that latter option is not viable as there tend to be all kind of variation usually from panel to panel due to many factors, difference in backlight led is common.
You keep assuming that there must be a unit-specific calibration of the display that is stored somewhere on the HD. There is not. This has been stated several times now, by several individuals.

Whatever you think is likely or unlikely is besides the point. Whatever approach is used, it is not stored as a configuration file somewhere on the HD.

My understanding is that the display manufacturer is obligated to deliver displays that meet Apple's specifications. If there is any sort of calibration process necessary to do that, the calibration data would be stored within the display module. Far more likely is that the manufacturing process is designed to meet tolerances, and those displays that fail the tests are rejected.

One thing I'm quite confident of - these are not the kind of "calibrated" displays a graphic arts or video producer might require. That kind of calibration requires separate software and a measuring device, and is done periodically over the life of the display because stuff changes over time. Those profiles are stored on HD, because they're not done by the manufacturer.
 
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BLBL

macrumors 6502a
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Apr 11, 2018
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Thanks for replies!

TM does backup the entire drive so is in effect a clone of the internal drive and it can be used to do a full restore, including the OS, apps, and all data and settings.
So TM backup can be also used as full restore to make OS exactly 1:1 as it was? Damn. I already reformatted that USB-drive before I saw your last post thinking it would not be full 1:1 image of my original hdd anyway (I got that impression from previous messages).

Anyway, I guess it does not matter since I got it back up and running even I wiped internal hdd and did internet based restore. I think I got pretty much everything installed what came with factory preinstalled OS but I still wonder what causes that I have now almost 10GB more free space? I know cache and all kind of garbage that gets collected in time eats hdd space but that was not the case here as it was brand new computer with just couple days use and hdd space did not much change during that from what it was after initial factory preinstalled OS setup other than some latest OS update downloaded and installed automatically (update that brought display brightness bump from 300 to 400 nits).
Any ideas what else than basic OS and "office apps" + GarageBand come with preinstalled OS. I added latter ones from App Store but am I still missing some programs or drivers?

If you want your TM backup encrypted, it is much faster to format the external drive to encrypted before using it with TM.
Thanks for confirming that. I had a hunch that might be the best approach in this case since I'll be starting with empty USB-drive anyway.

On the system drive, you do not want to format to encrypted. Just do a regular format the turn on FileVault afterwards.
Thanks, that is good to know. Any possible side effects from FileVault for performance or general reliability (I mean it is common to end up with corrupted more or less inaccessible drive, or is it simply robust?
Does FileVault usually cause long delay while it is encrypting data?


I get the feeling all this was a side point: The main point is you did all this because you're having an issue with your GPU and you were hoping a clean install would fix it, but it didn't.
Yes, you feeling is almost spot on. Issue with GPU was the final thing that drove me to do clean installation but I would have done that probably in any case as I explained earlier that this is my first Mac OS device and I've been learning to use it and tested all kind of things but not even logged to much any services that Apple offers (iCloud, FaceTime and so on) during initial setup. So after I got hang of the OS logic and have some understanding what I will do with the machine in the future, I wanted to setup up the fresh system from the beginning.

Anyway, I may have a clue what gives. I'll post my findings later on when I have verified that few times. I posted description and photos of this problem in another thread: https://forums.macrumors.com/threads/2018-air-screen-10-14-5.2181179/
I will add my latest finding there soon also. I have a hunch it is likely not just faulty panel but it has something to do with profiles or the way panel is "calibrated". It looks a bit like panel that has been pushed over what it is naturally capable of displaying. That's why I'm interested to learn IF these panels are someway individually adjusted and what kind of method is used and where it has been stored in case such is even used.

I'd consider making a genius bar appointment. I'm quick to point out Apple's faults, but the quality of their screens has always been top notch. If you see a noticeable visual issue, it's worth checking for a GPU problem.
No genius bars where I live. Only Apple phone support and repair centers but I have little faith on help those can provide in this kind of issue. Luckily I'm still within return window (I bough from shop with very long return period), so in case this turn out to be a faulty machine, I rather just take it back for refund than play lottery with service center.

You keep assuming that there must be a unit-specific calibration of the display that is stored somewhere on the HD. There is not. This has been stated several times now, by several individuals.

Whatever you think is likely or unlikely is besides the point. Whatever approach is used, it is not stored as a configuration file somewhere on the HD.
Maybe it is so as you keep saying. I'm just wondering that since they are able to even increase panel brightness by OS update (like Air 2018 got 300 to 400 nits) it obviously contain some data whether it is a driver or firmware update kind of thing they upload during setup so that they are able to control display hardware. You could upload correction tables for colors too to calibrate display.

My understanding is that the display manufacturer is obligated to deliver displays that meet Apple's specifications. If there is any sort of calibration process necessary to do that, the calibration data would be stored within the display module. Far more likely is that the manufacturing process is designed to meet tolerances, and those displays that fail the tests are rejected.
Maybe so, but obviously no one seems to know that for sure if, how or where possible calibration is saved. Or are these calibrated at all. Based on tests panels seem pretty much all calibrated the same way in each model, so hard to believe they just slap in a panel without adjusting them in any way. It would likely be very costly binning if only certain panels with correct colors/gray scale would be accepted.

One thing I'm quite confident of - these are not the kind of "calibrated" displays a graphic arts or video producer might require. That kind of calibration requires separate software and a measuring device, and is done periodically over the life of the display because stuff changes over time. Those profiles are stored on HD, because they're not done by the
manufacturer.
I know that they are not maybe pro video displays but they are one of the most accurate displays out there and I find it hard to believe it could be done by just slapping in panels straight out of productions line without individually adjusting them in any way.

I know individual calibration is well doable these days even on mass production without adding much cost.
For example Dell sells many display models that come individually factory calibrated and they each even come with calibration report. I have one of those Dell IPS models on my desk and it is very well calibrated an it was not expensive display at all and not much difference to similar non calibrated displays from other brands.
 
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BLBL

macrumors 6502a
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Another confusion with TM and encrypted USB hdd (external). I deleted USB hdd partition in disk utility and then created new journaled and encrypted disk. It makes is Corestorage (I guess that is right as there is no selection you can change).
But now when I set up TM it still asks whether I can to turn on encryption for backup or not? Should I also select that or is it already enough for having just whole disk encrypted (I mean would it be doing double encryption if both are in use)?

More confusion is that if I use externel USB hdd as just journaled non-encypted format and go to setup TM and there when it asks if I want to encrypt backup and then select yes, it will encrypt the whole HDD AND TM backup (you cannot select that TM encrypted on/off anymore)?

So why it lets have encrypted hdd and unencrypted TM backup when done in first way but not when done in second way? Confusing. :(
 

Weaselboy

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If you format an external drive to Mac OS Extended (Journaled, Encrypted) you will be asked for a password at that time. Go ahead and enter a password and erase the drive. Then eject the drive in DU. Now mount the drive in DU and you will get a popup asking for the password. Enter the password and check the box at the bottom to save the password in Keychain. Now when you attach the drive it will automatically unlock and mount. From then on you should be able to use it as a encrypted TM destination.

FV on your internal drive is very safe and will slow the drive a little on older Macs. If it is one of the newer T2 Macs there is almost no slowdown.
 

BLBL

macrumors 6502a
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OK. I already went ahead by making external drive as MAC OS Extended (journaled and encrypted) and set password for it. Then straight to TM and selected it for TM backup drive and checked Encrypt checkbox. I then ejected drive and connected again and it asks for password and opens the drive normal and shows up in TM too. I guess it should be allright by not using keychain and just input password each time I plug it in? Or should I have used Keychain for some particular reason (other than not needing to input password every time I use it)?

One thing I noticed was that icon color for the drive for some reason turn blue when I first time select it to use in TM as a backup drive but as soon as I eject the drive an then plug it back in, the icon color stays yellow as it was before selecting and setting it up as TM backup drive. Confusing. Any idea what logic is in that? I guess it does not matter but interesting behaviour as a usual Windows user... Still it seems to work and it is doing the first full TM backup as we speak.
 

Weaselboy

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Or should I have used Keychain for some particular reason (other than not needing to input password every time I use it)?
It just saves you the trouble of having to enter it each time.

The drive icon color change is normal.